我还没有弄清楚如何在Swift中获得字符串的子字符串:
var str = “Hello, playground”
func test(str: String) -> String {
return str.substringWithRange( /* What goes here? */ )
}
test (str)
我不能在Swift中创建一个范围。自动完成在游乐场不是超级有用的-这是它的建议:
return str.substringWithRange(aRange: Range<String.Index>)
我在Swift标准参考库中没有找到任何有用的东西。下面是另一个大胆的猜测:
return str.substringWithRange(Range(0, 1))
这:
let r:Range<String.Index> = Range<String.Index>(start: 0, end: 2)
return str.substringWithRange(r)
我看到了其他答案(在Swift字符串中查找字符索引)，似乎表明，由于字符串是NSString的桥类型，“旧”方法应该工作，但不清楚如何-例如，这也不工作(似乎不是有效的语法):
let x = str.substringWithRange(NSMakeRange(0, 3))
想法吗?
斯威夫特2.0
简单:
let myString = "full text container"
let substring = myString[myString.startIndex..<myString.startIndex.advancedBy(3)] // prints: ful
斯威夫特3.0
let substring = myString[myString.startIndex..<myString.index(myString.startIndex, offsetBy: 3)] // prints: ful
斯威夫特4.0
子字符串操作返回Substring类型的实例，而不是String。
let substring = myString[myString.startIndex..<myString.index(myString.startIndex, offsetBy: 3)] // prints: ful
// Convert the result to a String for long-term storage.
let newString = String(substring)
斯威夫特2
简单的
let str = "My String"
let subStr = str[str.startIndex.advancedBy(3)...str.startIndex.advancedBy(7)]
//"Strin"
斯威夫特3
let startIndex = str.index(str.startIndex, offsetBy: 3)
let endIndex = str.index(str.startIndex, offsetBy: 7)
str[startIndex...endIndex] // "Strin"
str.substring(to: startIndex) // "My "
str.substring(from: startIndex) // "String"
斯威夫特4
substring(to:)和substring(from:)在Swift 4中已弃用。
String(str[..<startIndex]) // "My "
String(str[startIndex...]) // "String"
String(str[startIndex...endIndex]) // "Strin"
这是你从字符串中获取范围的方法:
var str = "Hello, playground"
let startIndex = advance(str.startIndex, 1)
let endIndex = advance(startIndex, 8)
let range = startIndex..<endIndex
let substr = str[range] //"ello, pl"
关键在于您传递的是一个String类型的值范围。索引(这是advance返回的)而不是整数。
这是必要的原因，是因为Swift中的字符串没有随机访问(因为Unicode字符的长度基本上是可变的)。你也不能使用str[1]。字符串。索引的设计是为了与它们的内部结构一起工作。
你可以创建一个带有下标的扩展，这样你就可以传递一个整数范围(参见Rob Napier的回答)。
关于如何解决这个问题，已经有很多很好的例子。最初的问题是关于使用substringWithRange，但正如已经指出的那样，这比仅仅做自己的扩展更难。
上述范围的解决方案是很好的。你还可以用其他十几种方法来做到这一点。下面是另一个例子，告诉你如何做到这一点:
extension String{
func sub(start: Int, length: Int) -> String {
assert(start >= 0, "Cannot extract from a negative starting index")
assert(length >= 0, "Cannot extract a negative length string")
assert(start <= countElements(self) - 1, "cannot start beyond the end")
assert(start + length <= countElements(self), "substring goes past the end of the original")
var a = self.substringFromIndex(start)
var b = a.substringToIndex(length)
return b
}
}
var s = "apple12345"
println(s.sub(6, length: 4))
// prints "2345"
您可以使用这些扩展来改进substringWithRange
斯威夫特2.3
extension String
{
func substringWithRange(start: Int, end: Int) -> String
{
if (start < 0 || start > self.characters.count)
{
print("start index \(start) out of bounds")
return ""
}
else if end < 0 || end > self.characters.count
{
print("end index \(end) out of bounds")
return ""
}
let range = Range(start: self.startIndex.advancedBy(start), end: self.startIndex.advancedBy(end))
return self.substringWithRange(range)
}
func substringWithRange(start: Int, location: Int) -> String
{
if (start < 0 || start > self.characters.count)
{
print("start index \(start) out of bounds")
return ""
}
else if location < 0 || start + location > self.characters.count
{
print("end index \(start + location) out of bounds")
return ""
}
let range = Range(start: self.startIndex.advancedBy(start), end: self.startIndex.advancedBy(start + location))
return self.substringWithRange(range)
}
}
斯威夫特3
extension String
{
func substring(start: Int, end: Int) -> String
{
if (start < 0 || start > self.characters.count)
{
print("start index \(start) out of bounds")
return ""
}
else if end < 0 || end > self.characters.count
{
print("end index \(end) out of bounds")
return ""
}
let startIndex = self.characters.index(self.startIndex, offsetBy: start)
let endIndex = self.characters.index(self.startIndex, offsetBy: end)
let range = startIndex..<endIndex
return self.substring(with: range)
}
func substring(start: Int, location: Int) -> String
{
if (start < 0 || start > self.characters.count)
{
print("start index \(start) out of bounds")
return ""
}
else if location < 0 || start + location > self.characters.count
{
print("end index \(start + location) out of bounds")
return ""
}
let startIndex = self.characters.index(self.startIndex, offsetBy: start)
let endIndex = self.characters.index(self.startIndex, offsetBy: start + location)
let range = startIndex..<endIndex
return self.substring(with: range)
}
}
用法:
let str = "Hello, playground"
let substring1 = str.substringWithRange(0, end: 5) //Hello
let substring2 = str.substringWithRange(7, location: 10) //playground
